Deuteronomy 20:11

and if they answer you with words of peace, and open their gates to you, all the people whom you find therein shall be tributaries, and serve you.

TRIBUTARIES UNTO THEE, AND THEY SHALL SERVE THEE. “[Their surrender is not to be accepted] until they accept tribute and servitude upon themselves.” This is the language of Rabbeinu Shlomo [Rashi]. And in the Sifre the Rabbis have said: 200. “If they say ‘We accept tribute upon ourselves but not servitude’, or ‘servitude but not tribute,’ they are not to heed them until they accept both upon themselves.”
Now the purport of the tribute was that the king of Israel or the Sanhedrin could impose a levy upon them, [drafting men] to build the king’s palace and his store-cities, also the House of G-d. The servitude was that any Israelite could take one of them to be the hewer of his wood and the drawer of his water and pay him proper wages. This is the sense of what is written in connection with Solomon a levy of bondservants, meaning that they took upon themselves [both] tribute and servitude as is the law of the Torah. [However, the law of the Torah is] not as is written, And it came to pass, when Israel was waxen strong, that they put the Canaanites to tribute, but did not drive them out entirely, for “servitude” is not mentioned there. Instead it was like a king who bribes a more powerful king not to wage war against him.
Know that the matter of the Gibeonites came to pass because they did not know the law of Israel with respect to proclaiming peace, and therefore they put forward their plan, before Joshua’s proclamation arrived. Hence they said, and we were sore afraid for our lives., Verse 24. Or it may be that, at first they did not wish to hearken to Joshua’s offer [thus laying themselves open to invasion], and in the end they became frightened and disguised themselves as strangers, as it is written, And when the inhabitants of Gibeon heard what Joshua had done unto Jericho and to Ai, they also did work wilily., Verses 3-4. Their trickery helped them yet in that they did not become their servants, but their confederates.
The Israelites were irritated at them and would have killed them had it not been for the oath of the princes, Verse 19. because the Gibeonites should have taken upon themselves tribute and servitude, as we have said, while they [the princes] made a covenant with them to be equal and to be their confederates helping each other in their wars. They made peace with them [the Gibeonites] because they had thought that they were [from] very distant cities, from the peoples against whom they …